Ignition system for internal combustion engines

ABSTRACT

The primary winding of the ignition system includes two serially connected sections which are energized sequentially and form an effective means for storing energy in magnetic form.

United States Patent 11 1 [111 3,877,453

[22] Filed: Jan. 19, 1973 Brungsberg Apr. 15, 1975 IGNITION SYSTEM FORINTERNAL COMBUSTION ENGINES [56] References Cited [75] Inventor:Heinrich-Josef Brungsberg, UNITED STATES PATENTS Ludenscheid, Germany3,173,410 3/1965 McLaughlin 123/179 3,293,492 7/1963 Wald 315/180 [73]ASSlgl'lCBZ BIOWI'I, Rover! 81. C1e A.G., 3 709 20 H1973 123 14 EMannheim, Germany 3,731,144 5/1973 McKeown 315/209 T PrimaryExaminer-Manuel A. Antonakas [21] App]. No.: 324,945 AssistantExaminer-James W. Cranson Attorney, Agent, or FirmErwin Saltzer [30]Foreign Application Priority Data ABSTRACT Jan. 28, 1972 Germany 2203938The p y winding of the ignition system includes [52] U S Cl 123/148315/209 T two serially connected sections which are energized [51] F02)3/02 sequentially and form an effective means for storing [58] Field ofSearch 123/148, 179; 315/180, energy magnet: fOrm- 315/209 T 4 Claims, 2Drawing Figures PATENTEBAPR 1 5i9?5 SHEET 1 OF 2 PATENTEDAFR I 519. 5

SEZEU 2 BF 2 IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUNDOF THE INVENTION Among the various ignition systems for internal combustion engines the conventional transformer coil system is still usedmost extensively. This system is predicated on the storage of energy inmagnetic form but, as presently applied, has still three seriouslimitations:

1. Assuming that the life of the contact points of the interrupter issupposed to be in the order of, and not less than, about 6000 to 7000miles, this imposes a limitation on the current of the coil to the orderof about 4 Amps;

2. a limitation on the magnetically stored energy to the order of 30 to50 milliwatts sec.; and

3. a limitation of the time constant of the primary winding to a maximumvalue of about 6 milliseconds.

The inductivity of the primary winding is determined by the storedenergy and the maximum valve of the energizing current. In conventionaldesigns the inductivity of the primary winding is in the order of4 to 10millihenrys. The voltage of the d-c power supply or battery and themaximal admissible current determine the resistance of the primarywinding. Considering a d-c power supply or battery having a voltage of 6volts and considering the maximum permissible energizing current to be 4Amps, then the resistance of the primary winding is 1.5 Ohms. In thecase that the voltage of the do power supplies exceeds 6 volts aresistor is generally connected in series with the primary winding. Thetime constant of such an arrangement determined by the inductivity ofthe primary winding and its resistance are in the order of.2 to 6milliseconds.

To fully charge an inductance requires about three times the timeconstant. The charging time for standard ignition coils is, therefore, 3X 2 to 3 X 6 milliseconds, or 6 to 18 milliseconds. Considering that thecharging period of the ignition coil is limited to the time during whichthe contact points of the interrupter are separated which time is atmost 50% of the total cycle time for four cylinder engines leads to theconclusion that the full power of the ignition coil can only be obtainedup to an ignition or spark frequency of 80 Hertz.

A four cylinder internal combustion engine requires the above sparkfrequency of 80 Hertz at 2500 rpm. At higher numbers of revolution theignition energy decreases because there is not sufficient time availableto fully charge the inductance ofthe ignition system. Considering a fourcylinder internal combustion engine operating at full load at about 5500rpm which is quite common, the magnetic energy which is then stored, orcan be stored, in the coil system is about one-third of its possible ornominal value. The times during which the contact points of theinterrupter are closed and open, respectively, are even shorterconsidering six cylinder engines and eight cylinder engines rather thanfour cylinder engines and, therefore, the energy available for ignitionpurposes is relatively smaller as far as the former are concerned.

The above figures are based on the assumption that the voltage of thed-c power supply or battery is constant. This is, however, not alwaysthe case. There are instances, particularly the starting period of aninternal combustion engine, when the voltage of the d-c power supply orbattery is below normal. It must be kept in mind that the energy whichis available for ignition decreases when the voltage of the d-c powersource decreases.

Other important factors to be considered are the rate of rise of theignition voltage, and the breakdown value thereof. The rate of rise ofthe ignition voltage may be in the order of 350 volt/u sec. and thebreakdown voltage may be in the order of 10 to 15 kV. In cases where theinsulation level of the spark plugs is not sufficiently high,significant losses may occur during the entire rise time of the ignitionvoltage, thus decreasing the energy which is available for the purposeof ignition.

Transistorized coil ignition systems show a considerable improvementover the conventional, prior art or non-transistorizedignition systemswhich have been considered above. The former as well 'as the latter arepredicated on magnetic energy storage. The possibility offered bytransistors of switching relatively large currents without contacterosion by means of relatively small control currents resulted in anincrease of the life of the contact points of the interrupter. Theirlife is at present in excess of 30,000 miles. The advent of thetransistor made it also possible to substitute solid state circuitry forprior art mechanical switch means includ ing cam-operated contactpoints. Transistorized ignition systems make it possible to increase theprimary energizing currents of the coil system. This, in turn, resultsin a decrease of the time constant and an increase of the limitfrequency up to which the entire energy capable of being stored isstored in the coil system. These changes result in a decrease ofsensitivity in regard to changes of the voltage of the source of d-cpower. Application of transistors further results in a decrease ofswitching times and eliminates the problems of contact bounce, andtransistorized ignition systems for internal combustion engines do notrequire the shunt capacitors which form an integral part of moreconventional ignition systems. The former make it also possible toincrease the rate of rise of the ignition voltage to about 600 volts/ptsec. and this, in turn, decreases the effect of shunt current pathparallel to the spark gaps of the spark plugs. Transistorized ignitionsystems are, however, more expensive than more conventional coilignition systems.

Another relatively novel and unconventional ignition system for internalcombustion engines involves the use of electric energy stored in acapacitor rather than of magnetic energy stored in a coil system. Theoutput of a battery is supplied to an appropriate converter whose outputvoltage is much higher than its input voltage, e.g. 350 Volts. A storagecapacitor of about 1 ,u Farad is charged at the aforementioned elevatedvoltage and stores about 60 milliwatt-seconds. At the time of ignition,the aforementioned storage capacitor is discharged by the intermediaryof a thyristor into the primary winding of an ignition transformer orignition coil. The high capacitor discharge current results in a veryrapid rate of rise of the ignition voltage, e.g. at 8 kV/u sec. This hasthe beneficial effect of producing an acceptable ignition even if thespark plugs are not clean and have a relatively low insulating level,which is particularly important in regard to starting performance atcold days. A serious drawback of the aforementioned capacitor storageignition systems resides in the fact that the duration of the sparkdischarge is relatively short in comparison to the duration of thedischarge in conventional ignition systems. The duration of thehigh-voltage discharge in conventional ignition systems is in the orderof 1000 to 2000 u sec., but the duration of the high voltage dischargein the aforementioned ignition systems involving electrical storage in astorage capacitor is but 50 to 250 1.1. sec.

An up-dated novel ignition system for internal combustion engines wouldhave to meet with the following requirements:

l. The contact points of the interrupter should have a lifecorresponding to a mileage of at least about 30,000 miles. showing nosignificant deterioration or erosion at this time. The system should befurther able to allow substitution of the conventional interrupter by asolid state device, thus eliminating entirely relatively movablecontacts.

2. Even if the voltage of the d-c power supply declines as much as 50%,the value of the ignition energy should remain substantially unaffectedor unaltered.

3. The ignition energy should not deviate more than i from its normalvalue for the entire rpm range of the internal combustion engine.

4. The peak ignition voltage should be equal to, or larger than. 25kV(1'i 25 kV) and should have a rate of rise equal to, or in excess of,1 kV/ p. sec.

I 5. The igniting sparks should have a duration equal to, or in excessof, 500 p. sec.

6. The cost of the system should not significantly exceed those of aconventional coil ignition system.

It is the object of the present invention to provide an ignition systemwhich meets substantially with, or exceeds. the above requirements.

SUMMARY OF THE INVENTION tance section serially connected with saidfirst section.

The system further includes means for sequentially energizing said firstsection and said second section of said primary winding from a d-c powersource. To this end the ignition system includes switching means forinitially connecting said first section and said second section seriallyto said d-c power source. The system further includes a shunt-circuitby-passing said second section to allow energization by said d-c powersource of said first section only, which shunt-circuit includes atransistor for controlling the flow of current therein. A tertiarywinding is inductively coupled with the primary winding and provides thecontrol current for said transistor. In addition systems embodying thisinvention include a diode arranged to preclude current flow in saidsecond section while said first section is being energized by a currentflowing through said transistor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a wiring diagram of a systemembodying the present invention including one control transistor; and

FIG. 2 is a wiring diagram of a system embodying the present inventionincluding two control transistors.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings,numeral 10 has been applied to indicate a d-c power supply, or battery,to energize the ignition system. Reference numeral 7 has been applied togenerally indicate an induction coil. The latter includes the secondaryor high-voltage winding 5 and the primary or low-voltage winding 6.Windings 5 and 6 form an autotransformer. The low-voltage or primarywinding 6 is subdivided into two serially connected sections 3 and 4.The first section 3 has a relatively small resistance and the secondsection 4 has a relatively high resistance. One electrode of each sparkplug 9 is grounded and the other electrode of each spark plug 9 isconnected by a lead to the upper end of high-voltage winding 5. Thenegative pole of battery 10 is grounded and connected by a lead to theupper end of winding section 3.

FIG. 1 shows in the right upper portion thereof four spark plugs 9 whichmay be periodically conductively connected to the upper end ofhigh-voltage winding 5 by means of a rotating distributor shown at theleft of the spark plugs 9. Switch 1 is operated by means of a cammounted on the same shaft as the distributor for the four spark plugs 9.The system includes a tertiary winding 11 inductively coupled with theprimary winding 6. The flow of current from the positive pole of battery10 to the point intermediate winding sections 3,4 is controlled byswitch 2 and by a solid state gate, preferably a transistor 12. Tertiarywinding 11 supplies the base current for transistor 12, and thuscontrols the flow of current 13 from the positive pole of battery 10 tothe point intermediate winding sections 3 and 4. The positive pole ofbattery 10 is further connected by a lead including cam-operated switch1 and diode 8 to the bottom end of winding section 4.

The above circuitry or system operates as follows:

When interrupter contact 1 closes an initial current is allowed to flowfrom the positive pole of battery 10 through closed switches 2 and 1,diode 8, and winding sections 4 and 3 of primary winding 6 to thenegative pole of the battery 10 which is grounded. This initial currentinduces a voltage in the tertiary winding 11, as a result of which acurrent i is caused to flow unblocking transistor 12. Hence a currentpath for the charging current i of winding section 3 is established.This current path extends from the positive pole of battery 10 throughswitch 2 and transistor 12 to the point intermediate winding sections 3and 4 and then through winding section 3 to the negative pole of battery10. The charging current rises linearily to a predetermined peak valuewhich may be 12 Amps. When this value is reached, the common core ofwindings 5, 6 and 11 is saturated. As a result, the flow of gatingcurrent i ceases and transistor 12 returns from its conductive state toits current blocking state. During the charging period of windingsection 3 a voltage was induced in winding section 4 but could notresult in a current flow through winding section 4 on account of thepresence of blocking or reversed biased diode 8. When the current flowthrough winding section 3 ceases the backvoltage in winding sectiondecays to zero and a current flow is established from the positive poleofbattery 10 through switch 1 and diode 8 then biased in forwarddirection and through the serially connected winding sections 4,3 to thenegative pole of battery 10. This current which may be referred to asholding current i maintains the core of windings 5,6 and 11 in a stateof saturation. Holding current i appears without time delay and themagnetic energy originally stored in the system remains unchanged.

Opening of switch 1 results in a conversion of the magnetic energystored in the system into electric energy, i.e. a flow of currentthrough the high-voltage circuit including high-voltage winding 5, therotary distributor connecting the latter and the four spark plugs 9 andone of the four spark plugs 9. In the circuitry of FIG. 2 opening ofswitch 1 may result in arcing at this point. This tends to reduce therate of rise of the highvoltage across the ends of high-voltage winding5 as a result of the dissipation of a portion of the magnetic energystored in the system in form of are energy. The circuitry of FIG. 2 isnot subject to this limitation.

In FIG. 2 the same reference characters as in FIGS. 1 have been appliedto indicate like parts. Hence a description of FIG. 2 can be limited tothe features distinguishing the circuitry of FIG. 2 from that of FIG. 1.The former includes an additional solid state gate or transistor 13inserted into the lead from the positive pole of battery and switch 2 tothe lower end of winding section 4 including diode 8. Switch 1 controlsthe gate current path or base current path of transistor 13 whichcurrent path includes resistor 14 and the Zener diode 15. Thustransistor 13 is arranged to carry the holding current i, or I andswitch 1 controls but the gating or base current for transistor 13. Thecircuitry of FIG. 2 operates as follows:

Closing of switch 1 supplies transistor 13 with sufficient base currentto allow the flow of an initial current i,=i from the positive pole ofbattery 10 through winding sections 4 and 3 in series to the negativepole of battery 10. This initial current causes energization of tertiarywinding 11 and the resulting current unblocks transistor 12. Thisestablishes a path for loading current i from the positive pole ofbattery 10 through transistor 12 to the point of intermediate windingsections 4 and 3 and through winding section 3 to the negative pole ofbattery 10. The current through winding section 3 increases linearilyto, say, l2 Amps. when the core of windings 5 and 6 is saturated,tertiary winding 11 de-energized and transistor 12 returned to itsblocking condition.

The charging current i of winding section 3 induces an emf in windingsection 4 not resulting in a flow of current in winding section 4 onaccount of the blocking action of diode 8. Upon disappearance of saidemf holding current 1'. immediately, i.e. without time delay, maintainsthe energization of auto transformer 7 which remains in a state ofsaturation. Upon opening of switch 1 the magnetic energy stored in thesystem results in the flow of current in the circuit including winding 5and one ofthe four spark plugs 9. The presence of transistor 13 makes itpossible to minimize the currents to be switched by switch 1 and tosubstitute, if desired. a

non-mechanical or solid state switch for the mechanical switch 1. Theinductance of winding 5 may be kept relatively small yet resulting in arise of voltage larger than 1 kV/usec. and in a peak voltage larger than25 kV. Changes in the voltage of battery 10 up to 50% and in the numberof revolutions of the internal combustion engine have no effect upon theenergy supplied for ignition purposes. Resistor l4 and Zener diode 15limit the holding current I I claim as my invention:

1. An ignition system for internal combustion engines comprising a.means forming a high-voltage circuitry including spark plug means (9)and a secondary winding (5);

b. means forming a low voltage circuitry including a primary winding (6)inductively coupled with said secondary winding (5), said primarywinding (6) having a first small resistance section (3) allowing rapidbuild-up of current therein and a second high resistance section (4)serially connected with said first section (3);

c. switching means (1) for initially connecting said first section (3)and said second section (4) serially to said d-c power source;

d. a shunt-circuit by-passing said second section (4) to allowenergization by said d-c power source (10) of said first section (3)only, said shunt-circuit including a transistor (12) for controlling theflow of current therein;

e. a tertiary winding (11) inductively coupled with said primary winding(6) and providing the control current for said transistor (12); and

f. a diode (8) arranged to preclude current flow in said second section(4) while said first section (3) is energized by a current flowingthrough said transistor(l2).

2. An ignition system as specified in claim 1 wherein said switchingmeans for initially serially connecting said first section (3) and saidsecond section (4) to said d-c power supply include a secondtransistor(14).

3. An ignition system as specified in claim 2 wherein a resistor and aZener diode are connected in series with said second transistor, andsaid first section (3) and said second section,(4) of said primaryWinding (6).

4. An ignition system as specified in claim 1 wherein said primarywinding (6) has a tap arranged between said first section (3) and saidsecond section (4) thereof, wherein the emitter of said transistor (12)and one end of said tertiary winding (11) are connected to said tap, andwherein the other end of said tertiary winding (11) is connected to thebase of said transistor (12).

1. An ignition system for internal combustion engines comprising a.means forming a high-voltage circuitry including spark plug means (9)and a secondary winding (5); b. means forming a low voltage circuitryincluding a primary winding (6) inductively coupled with said secondarywinding (5), said primary winding (6) having a first small resistancesection (3) allowing rapid build-up of current therein and a second highresistance section (4) serially connected with said first section (3);c. switching means (1) for initially connecting said first section (3)and said second section (4) serially to said d-c power source; d. ashunt-circuit by-passing said second section (4) to allow energizationby said d-c power source (10) of said first section (3) only, saidshunt-circuit including a transistor (12) for controlling the flow ofcurrent therein; e. a tertiary winding (11) inductively coupled withsaid primary winding (6) and providing the control current for saidtransistor (12); and f. a diode (8) arranged to preclude current flow insaid second section (4) while said first section (3) is energized by acurrent flowing through said transistor(12).
 2. An ignition system asspecified in claim 1 wherein said switching means for initially seriallyconnecting said first section (3) and said second section (4) to saidd-c power supply include a second transistor(14).
 3. An ignition systemas specified in claim 2 wherein a Resistor and a Zener diode areconnected in series with said second transistor, and said first section(3) and said second section (4) of said primary winding (6).
 4. Anignition system as specified in claim 1 wherein said primary winding (6)has a tap arranged between said first section (3) and said secondsection (4) thereof, wherein the emitter of said transistor (12) and oneend of said tertiary winding (11) are connected to said tap, and whereinthe other end of said tertiary winding (11) is connected to the base ofsaid transistor (12).